«Open Season (Joe Pickett 1)» by C.J.Box

Winner of the Anthony Award for Best First NovelWinner of the Gumshoe Award for Best First NovelWinner of the Barry Award for Best First NovelWinner of the Macavity Award for Best First Novel
There's nothing unusual about the sound of a gunshot in Twelve Sleep. Here in remotest Wyoming, where elk roam the pine forests and cougars prowl the mountains, everyone owns a gun. But when Joe Pickett hears two sharp cracks ring out months before hunting season, it's his job to investigate.
As game warden in Twelve Sleep, father-of-two Joe Pickett is not only badly paid and poorly housed, but deeply unpopular. So when the source of the shots – a well-known poacher – gets off scott-free after a humiliating confrontation, the locals are delighted.
And then the poacher turns up dead in the Pickett's backyard.
Charged with investigating the first murder he's ever encountered, Joe soon finds himself swamped with questions. How did the dead man get to his house? What was in the empty cooler by his side? And why do his colleagues want to sweep the case under the rug? Battling grudge-holding neighbours, corrupt officials and out-of-town activists, Joe begins to unravel a mystery that threatens the life and the family he loves.